Thermal retarder



Jan. 8', 1946. c. M. osTERHELD 2,392,498

THERMAL RETARDER Filed March 22,' 1944 @wg-, im@

ATTORNEY Patented Jan. 8, 1946 UNITED STATES PATENT oFFIcE THERMAL RETARDER Clark M. Osterheld, Stoughton, Wis., assignor to McGraw Electric Company, Elgin, Ill., a corporation of Delaware Application March 22, 1944, Serial No; 527,582

14 Claims.

My invention relates to electric heating and particularly to control means therefor.

An object of my invention is to provide a relatively simple form of thermal retarder heater control switch adapted to cause energization of an electric heater of a domestic hot water tank either immediately or with a predetermined time period of delay in accordance with the amount of hot water withdrawn from the tank.

Another object of my invention is to provide a relatively simple and 'inexpensive' thermal re'- tarder heater control switch unit adapted to cause energization of the electric heater of a hot water tank with a predetermined time period of delay in case of use vof only a relatively'small amount of hot water from the tank fto bring the time of energization into the periods of relatively small loads on the electric supply circuit.

Other objects of my invention will either be apparent from a description of a device embodying my invention or will be pointed out in the course of such description and be set forth in the appended claims.

In the drawing: l

Figure 1 is a vertical sectional view of a domestic hot water tank, having associated therewith a device embodying my invention,

Fig. 2 is a view in side elevation thereof with the casing shown in section,

Fig. 3 is a top plan view thereof,

Fig. 4 is a view in front elevation thereof, and

Fig. 5 is a diagram of connections.

Referring first of all to Fig. 1 of the drawing, I have there shown a domestic hot lwater tank II having a lower cold water vinlet pipe I3, an upper hot water outlet pipe I5, heat insulation Il, such'as rock wool around the tank Il, the heat insulation Il being held in proper operative.position by an outer casing I9.

y I provide preferably, but not necessarily, a single electric heater ZI positioned at the lower end l r of the tank II and located in a tunnel 23. As shown in Fig. 1, the electric heater 2l `is a clampon heater, although I do not desire to be limited thereto.

I provide a lower thermally-actuable heater control switch including a tubular member 25 having a closed inner end and having its open outer end secured in an opening in tank II near the lower end thereof in a fluid-tight manner. Within the tubular member 25 I provide an expansion rod 2 adapted to engage with and be disengaged from a resilient contact arm 23 which is adapted to engage with and be disengaged from a rigid contact arm 3l, the two contact arms AESG being supported as by blockso33 of electric-insulating material on. the tank Il. While I have shown and described a particular form of thermally-actuable heater control switch positioned at the lower end of tank II, I do not desire to be limited thereto, since other equivalent forms of heater control switches may be used instead.

Referring now to Figs. 2, 3 and 4 I have there shown the device embodying my invention as comprising a casing 35 of heat-conducting material adapted to contain a thermal retarder heater control switch unit designated in itsentirety by numeral 3l. The casing 35, while shown as having a level rear surface, is adapted to be mounted on the tank II in heat-receiving relation thereto at substantially the mid-portion of tank II. Since the tank II has an arcuate outer surface, I may employ an intermediate support of heat-conducting metal or alloy.

'I'he thermal retarder unit includes a rst high-expansion bimetal bar 39 having its lower end portion thereof secured to a supporting block 4I! suitably secured to the rear wall of casing 3'5 as by one or several short machine screws 4I extending through the lower portion of the bimetal bar 39. At the upper free end of bar 39 I provide a bracket 43 of substantially channel-shape adapted to have a pivot pin 45 extending therethrough.

I provide a block 41 of heat and electric-insulating` material suitably secured against say the bottom wall of casing 35 and adapted to have mounted thereon a bracket 48, of L-shape, held by a screw 49, to which bracket is secured the lower end of a second bimetal bar 5I. The second bimetal bar 5I has a thermal expansivity on the order of one-half that of bar 39, which result may be obtained ,by making the thickness of the first bimetal bar 39 on the order of .025", while the thickness of the second bimetal bar 5I may be on the order of .070", or by making the bar 5I of lesser thermally-responsive material. The upper free end of bar 5I has mounted thereon a bracket 53 of channel shape in section adapted to have a pivot pin 55 extend through the parallel end-portions thereof. I provide.electric-insulating material 5i? around the greater length of bimetal bar 5I and position thereon a heating coil 59, the wattage input whereof is on the order of only a few watts.

A switch actuable by the two bimetal bars 39 and 5I when in operation includes a first upper 'toggle arm 5I, which toggle arm includes a first 2 v I i i tending portion 95 and a 'third substantially ver.

, |03 by a conductor I 300 F. before tically extending portion 91. The-portion 93 is provided with an enlarged lower end 69 having an 5 opening therein through which pin l5 is adapted toggle arm 5| and an over-center spring has its upper portion located `in an elongated recess in part 61 and its upper end connected to part 31 while its lowerend portion is positioned in anv lled with cold water, with the result that'thc elongated recess in arm 11, the lower end portion of spring 19 engaging the arm 11 at the end of therecess.

A contact bridging mountedon the lower end of the second toggle arm 11 vand is adapted to engagel'with a pair of contact members 33 and 85 which are insulatedly supported by a bracket 81 of generally channel shape-in section secured to the upper surface of block 41 as by screws 88. Terminalconnectors 9| are insulatedly supported againstthe inner end portion ofbracket 31 as by nuts 93 engaging the body portion of the contact members 93 and 85.

u A stop means for the lower toggle arm 11 includes a stop screw 95 having screw threaded engagement with the outer end portion of-member 81,

V.a lock nut 91 being provided to hold. the stop screw 95 in a given position. A'cover 99 is provided for the casing 35 and may be held in proper operative position thereon by any suitable or desired means.

A Referring now to Fig. 5 of the drawing, I 'have there shown `a diagram of'connections used in and with my improved vheater control system. A

ypair of continuously energized supply circuit conductorsi and |03 are provided, supply circuit conductor i0! being connected by a conductor |05 with contact terminal 85. .The other contact terminal 891s connected by a conductor |01 with one terminal of heater 2|, the other terminal of which is connected to the substantially'rigid contact arm 3|. A conductor |09 connects the rigid contact arm 3| with one terminal of heating coil 59. the other terminal of which is connected by a conductor to contact 95. Resilient contact arm 291s connected to supply circuit conductor 3. v It maybe here pointed out that thetemperature or the ilrst bimetal bar 39 'will'be subject to that of the water in the tank `When cold 'memberi is insulatedly y water is referred to,'water at a temperature of or '10 F. is meant, while when reference is made to hot water, a temperatureof 150 F. or `slightly higher is meant. The temperature of the rst high expansion bimetalbar 39wil1 therefore have a range of vfrom 65 F. to150 F. and

is-designed, constructed, and vadjusted to be sub-v stantially straight at 6,5? F, or '10 F.. as shown in full lines in Fig. 2, and will be exed to substam-.rally the position shown in broken unes in Fig. 2 when its temperature is on the order` of 1509 F. When the second bimetal bar 5| is at a. temperature of 65? to '10 F., it will be substantially straight, as shown in lull lines in Fig. 2, and will ilex in a counterclockwise direction when through as great a distance as did the free end oi bimetal bar 39 when the latter washeated t0 a temperature of 150F. This heating is eiected by the heating coil 59 and willrequire a length of time on the order oi.' ve to six hours. When "the temperature of the two bimetal bars is at ordinary room value (65. F., to 70 F.) the switch controlled thereby will be closed; when the temperature of the two bars is at 150 F., the switch willjbe open; and when the temperature of the iirst bar is 150 F. andv the temperature of the second bar -is 300 F., the switch will be closed.

Let is .now' be assumed that the tank is ilrst gized. Since the lower thermally-actuable heater control switch controls the energization of the heating coil 59, this heating coil will be energized, causing temperature rise of the second bimetal bar 5|. As was` hereinbefore stated, the

amount of electric energy translated into heat in heating coil 59 is relatively small, andit may take sir;4 hours to cause the maximum operative temperature rise of the second bimetal bar 5| to occur.

' When starting with a tank entirely lled with cold water, the temperature of the water is quite uniform from top to bottom of the tank during the heating-up period so that the temperature rise of the water from '10 F. to 150 F. will be accompanied by a similar rise in temperature of` bimetal bar 39. The energized coll 59 will also cause a temperature rise of the second bi- .metal bar 5|, and if it requires say six hours toA heat all of the water in the tank to150 F., the 'switch will remain closed during the entire time, and deenergization of the heater 2| will be effected by the lower thermally-actuable switch when it is subject to hot water. This deenergization of the control system will also deenergize the heating coil 59, with the result that the toggle arm 11 will move to its open position, remaining in suchposition until a change of temperature conditions of the thermal switch occurs.

Let it now be assumed that a predetermined amount of hot water is withdrawn from the tank,

this amount being sufcient to cause subjection of tubular member 25 to cold water'. The attendant closure ,of the lower thermallyeactuable switch will effect energization of the heatingcoil 59 with attendant temperature rise of the second bimetal bar, which bar will reach its maximum Y operative temperature in from say fourv to six 6d hours, whereupon the thermal retarder heater control switch will again be moved into closed,

heater-energizing position. .Reenergization of heater 2| will therefore take place and will continue until' all of the water is again hot.

Let it now be assumed that a greater amount of hot water was withdrawn from the tank so that the amount of cold water entering the tank is sufilcient to aiect the thermal retarder switch unit mounted at substantially the midi-height of the tank, with attendant quick closure of the heated. Since its thermal expansiv'ity is only switch controlled by the thermal retarder and reenergizationof heater 2| and of heating coil 59. Energization of heater 2| will continue until the dividing line between the hot and the cold waterfwill have been moved down below the thermal retarder', when the thermal retarder switch will be opened to deenergize the heater 2 I. After a period of time suilicient to heat the second bimetal bar 5l to its maximum operating value, the thermal retarder switch will again be closed, 'energization of heat 2| will again be eiected and will be continued until substantially all of the water in the tank is hot, when the lower thermally-actuable switch will be opened.

The thermal retarder embodying my invention is therefore effective to ensure that there shall be available at all times at least a half tankful of hot water. In case the tank contains only a small amount of cold water, say `a quarter tankful, because of use of hot water in the early morning or late afternoon and early evening hours, energization of the heater will be delayed until the oil-peak periods of early afternoon and late night hours.

It isevident that if a predetermined amount of cold water enters the tank, just suilicient to affect only'the lower thermal heater control switch,

` reenergization of the electric heater will take device embodying my'invention, and all such modifications clearly coming within the scope of the appended claims shall be considered as being covered thereby. Y

I 'claim as myinvention:

1. A thermal retarder switch unit for hot waterstorage heaters comprising two normally straight bimetal bars and a switch operated by `change in relative thermal condition of the two bars, one of said bars being subject to heat exchange with water in the tank and means independent-of the tank and of the position of said switch for exchanging heat with the other bar.

a diierent point than the other, means for con necting one of said bars for heat exchange with water in the tank and independent means for changing the temperature of the other bar irrespective of the position of said switch arm.

7. A thermal retarder switch unit for a hot water storage tank heater comprising a switch 2. A thermal retarder switch unit for hot t water storage heaters comprising a switch lever and two bimetal bars acting mechanically upon the switch lever at different points, one of said bars being subject to heat exchange with water in the -tank and the other being subject to heat independent of the tank and cf the position of said switch lever.

3. A thermal retarder switch unit for hot water storage heaters comprising a switch lever and two bimetal bars acting mechanically on the switch lever at spaced points, means for thermally connecting one of said bars with the tank for heat exchange with the tank water, and means for heating the other bar directly independent of the tank water and of the position of said switch lever.

4. A thermal retarder switch unit for hot water storage tank heaters comprising a switch lever, two bimetal bars of different thermal expansivities acting mechanically on said switch lever at different points, means vfor thermally.

arm, two bimetal bars of different thermal expansivities pivotally supporting and acting on said switch arm at spaced points, means for connecting one of said bars for heat exchange with water in the tank and independent means for changing the temperature of the other bar irrespective of the position of said switch arm.

8. A thermal retarder switch unit for hot water .storage tank heaters .comprising a switch lever,

two bimetal bars of different thermal expansivities acting on said switch -lever at different points, means for thermally connecting the bar of greater thermal expansivity with tank water and means for heating the other bar directly independent of tank waterl said switch lever being adapted to be in closed position when both bars are at ordinary room temperature, to be in open position when the bar of greater thermal expansivity is at; a, temperature on the order of F. and the second bar is at ordinary room temperature and to be in closed position when said bar of greater thermal expansivity is at a temperature on the order of 150 F. and said second bar is at a temperature on the order of 300 F.

9. A thermal retarder switch unit for a hot water storage tank heater comprising a rst bimetal bar oi.' high thermal-expansivity, a second bimetal bar of lower thermal expansivity, a heatconducting support for said two Vbars to hold them at one end thereof and extending substantially parallel to each other, said support being adapted to be mounted on a tank in heat conducting relation therewith, an electric heating coil for said second bar and a switch arm Divotally engaged by said two bars at two different points and adapted to be moved into circuit closing position when both bars are at ordinary room temperature, to be moved into open circuit position when said rst bar is subject to hot water in the tank and said heating coil has been energized for less than a predetermined length of time and to be moved into closed position when said first bar is subject to hot waterin the tank and said heating coil for said second bar has been energized for at least a predetermined length of time.

10. A thermal retarder heater control switch unit for a heater of a hot water tank, comprising a high expansion bimetal bar adapted to be mounted in heat-conducting relation to the tank, a low-expansion bimetal bar, a heating coil for said low-expansion bar and a heater control switch actuable jointly by said two bimetal bars into closed position when said high expansion bar is subject t`o cold water in the tank and said heating coil has been energized for less than a predetermined length of time, to be moved into open position when said high-expansion bar is subject to hot water and said heating coil has length of time and to be moved into .closed position with a predetermined time delay period when 4said high-expansion bar is subject to the temperatureof hot water and said heating coil has been energized. v

11. A thermal retarder heater control switch unit for a heater'ofa hot water tank, compris' ing a high expansion bimetal bar adapted to l `be mounted in heat-conducting relation to the tank, a low-expansion bimetal bar, a heating said high expansion bar is subject to the temperature of hot water in the tank and said heating coil has raised the temperature of said low expansion bar to a predetermined value higher than that of said high expansion bar.

.12. A thermal retarder switch unit for controlling the energization of an electric heater circuit for a hot water tank, comprising a switch,

va high-expansion bimetal bar adapted to be thermally connected with the tank for heat exciably higher temperature.

, been energized for less than a predetermined change with vthe water in the tank. a low-expansion bimetal bar and an electric heating coil for said low expansion bar energizable by power from said circuit for heating saidlow-expansion bar irrespective of the position of said switch.

'13. A Water heaterl control system for a domestic hot water tank having an electric heater,

comprising a thermally-actuable switch adapted to deenergize said heaterv when substantially all of the water in the tank is hot and a bimetal thermal retarder switch mounted on the tank between the ends thereof and comprising a pair of dissimilarly thermally-actuable elements to prevent energization of said heater until after elapse of a. predetermined length of time after entry of a predetermined relatively small quantity of cold water into the tank.

14. A thermal retarder switch unit for hot water storage tank heaters comprising a-switch lever, two bimetal bars of' diierent thermal expansivities acting on said switch lever at aiierent points, means for thermally connecting the bar of greater thermal expansivity with tank water and means for heating the other bar directly independent of tank water, said switch lever .being adapted to be in open position when both bars are at substantially the temperature of about 150 F. and to be in closed position when the bar of greater thermal expansivity is at a tempera.- ture of 150 F. and the other bar is! at an apprei CLARK M. OSTERHEID. 

